Lighting power supply system and method

1. A power supply system to be used with a lighting unit, comprising: a driver adapted to receive an AC or DC input power supply at an input, and to convert the input power supply into a driving current at an output for supply to the lighting unit; an interface to an energy storage device for providing an secondary power supply; a converter adapted: in a first mode to connect to said output of said driver for diverting at least a part of the driving current from the lighting unit to charge the energy storage device; in a second mode to connect to the lighting unit for converting the secondary power supply to drive the lighting unit; and in a third mode to drive the lighting unit from a grid at the input without charging or discharging the energy storage device; and a controller to actively control said converter and the output of said driver synchronously to maintain the current through the lighting unit when switching the converter between the third mode and one of the first and second modes, wherein the controller, when to actively control said converter and the output of said driver synchronously when switching the converter between the third mode and the second mode, is adapted to: obtain an output of the converter, and control the output of the driver according to the obtained output of the converter; or obtain an output of the driver, and control the output of the converter according to the obtained output of the driver.

2. The system as claimed in claim 1 , wherein the lighting unit comprises an LED arrangement, the driver comprises a current source LED driver with an output connectable to the LED arrangement, and in the first mode the converter is adapted to be in parallel with the LED arrangement, wherein the controller is adapted, when to obtain an output of the converter, and control the output of the driver according to the obtained output of the converter, is adapted to: a) control the converter to output an output voltage to reach a voltage threshold of the lighting unit while said driver to output the driving current, and then control the driver not deliver the driving current, synchronously with the converter to output the driving current; or b) inject current into the lighting unit from the driver and the converter simultaneously; sense, in a control loop of the driver, the total current through the lighting unit including the output current of the converter; change the output current of the converter; and allow the control loop of the driver to change an output current of the converter to maintain the total current.

3. The system as claimed in claim 1 , wherein the controller is adapted, when to obtain an output of the driver, and control the output of the converter according to the obtained output of the driver, to: c) inject current into the lighting unit from the driver and the converter simultaneously; sense, in a control loop of the converter, the total current through the lighting unit including the output current of the driver; change the output current of the driver; allow the control loop of the converter to change an output current of the converter to maintain the total current.

4. The system as claimed in claim 2 , wherein the power supply system is operable in: a first state in which the driver is adapted to deliver the driving current to the lighting unit, and the converter is adapted to, in the third mode, not operate; a second state in which the driver is adapted to deliver the driving current to the lighting unit, and the converter is adapted to be in a start-up mode during which the converter is adapted to output a converter output voltage and increase a conversion ratio of the converter until the converter output voltage reaches a voltage threshold of the lighting unit; and a third state in which the converter is adapted to output the converter output voltage that has reached the voltage threshold of the lighting unit and to proceed to operate in the second mode, and the driver is adapted to not deliver the driving current, synchronously.

5. The system as claimed in claim 4 , wherein in the third state, the converter is adapted to increase the conversion ratio until the driving current through the lighting unit in a preceding first state is restored in the second mode.

6. The system as claimed in claim 4 , wherein the controller is adapted to switch the system between the first, second and third states in response to a high demand duration in the input power supply or to a demand response call from a utility providing the input power supply.

7. The system as claimed in claim 4 , the power supply system is operable in: a fourth state in which the converter is adapted to deliver the driving current in the second mode, and the driver is adapted to not deliver the driving current; a fifth state in which the converter is adapted to deliver the driving current to the lighting unit, and the driver is adapted to be in a start-up mode during which the driver is adapted to output a driver output voltage to reach the voltage threshold of the lighting unit; and a sixth state in which the driver is adapted to deliver the driving current to the lighting unit, and the converter is adapted to, in the third mode, not operate.

8. The system as claimed in claim 1 , wherein the power supply system is operable in: a first state in which the driver is adapted to deliver the driving current to the lighting unit, and the converter is adapted to, in the third mode, not operate: and a seventh state in which the controller is adapted to instruct the driver to increase the driving current at the output, and to instruct the converter to start to operate in the first mode, synchronously; wherein the converter is adapted to, in the first mode, detect the current through the lighting unit, and tune the part of the driving current from the driver diverted from the lighting unit to charge the energy storage device such that the current through the lighting unit is still constant.

9. The system as claimed in claim 8 , wherein the controller is adapted to operate the system from the first state to the seventh state in response to a low demand duration in the input power supply.

10. The system as claimed in claim 8 , wherein the controller is adapted to instruct the driver to increase the driving current at the output step by step, and to instruct the converter to increase the part of the driving current from the driver diverted from the lighting unit step by step, and the power supply system is operable in an eighth state in which the controller is adapted to instruct the driver to decrease the driving current at the output step by step, and to instruct the converter to decrease the part of the driving current from the driver diverted from the lighting unit step by step, synchronously.

11. The system as claimed claim 1 , wherein the converter is a bi-directional switched mode power converter.

12. The system as claimed in any claim 11 , wherein the converter is a bi-directional buck/boost converter wherein the converter is a buck converter from the output of the driver to the energy storage device and is a boost converter from the energy storage device to the lighting unit.

13. The luminaire comprising: a lighting unit; and a power supply system as claimed in claim 1 .

14. The lighting system comprising: a plurality of luminaires each as claimed in claim 13 ; a plurality of energy storage devices, each associated with a respective luminaire via the interface; and a remote server to communicate with the controller of the power supply system of each luminaire.

15. The lighting system according to claim 14 , wherein said remote server and said controller are adapted to communicate via a wireless protocol, and said wireless protocol comprises ZigBee protocol, and the lighting system further comprises: a ZigBee gateway adapted to connect said remote server via a wired network, and connect to said controller via the ZigBee protocol; and wherein said controller of said luminaire comprises a DALI module to receive command in ZigBee protocol and to control the driver and the converter via DALI protocol.